BS-7820-1-1995 ISO-10727-1995.pdf
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1、BRITISH STANDARD BS 7820-1: 1995 ISO 10727:1995 Analysis of tea and tea products Part 1: Tea and instant tea: determination of caffeine content Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:29:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7820-1:1995 Thi
2、s British Standard, having been prepared under the direction of the Consumer Products and Services Sector Board, was published under the authority of the Standards Board and comes into effect on 15 June 1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee refe
3、rence AW/8 Draft for comment 91/52732 DC ISBN 0 580 24194 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee AW/8, Tea, upon which the following bodies were represented: Campden and Chorleywood Food Research Association Mi
4、nistry of Agriculture, Fisheries and Food Natural Resources Institute Tea Trade Technical Committee United Kingdom Tea Association Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:29:34 GMT+00:00 2006, U
5、ncontrolled Copy, (c) BSI BS 7820-1:1995 BSI 10-1999i Contents Page Committees responsibleInside front cover National forewordii 1Scope1 2Normative references1 3Principle1 4Reagents1 5Apparatus1 6Sampling2 7Preparation of test sample2 8Procedure2 9Calculation3 10Precision3 11Test report3 Annex A (in
6、formative) Results of interlaboratory test4 Annex B (informative) Bibliography4 Table A.1 Repeatability and reproducibility values4 List of referencesInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:29:34 GMT+00:00 2006, Uncontrolled Copy, (c
7、) BSI BS 7820-1:1995 ii BSI 10-1999 National foreword This Part of BS 7820 has been prepared by Technical Committee AW/8 and implements an agreement, to which the UK was a party, reached in Subcommittee 8, Tea, of Technical Committee TC 34, Agricultural food products, of the International Organizati
8、on for Standardization (ISO). The UK also provides the secretariat for the Subcommittee. This Part of BS 7820 is identical with ISO 10727:1995 Tea and instant tea in solid form Determination of caffeine content Method using high-performance liquid chromatography. A British Standard does not purport
9、to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references Publication referred toCorresponding British Standard ISO 15
10、72:1980BS 6049 Methods of test for tea Part 1:1981 Preparation of ground sample of known dry matter content (Identical) ISO 1839:1980BS 5987:1980 Methods for sampling tea (Identical) ISO 3696:1987BS 3978:1987 Specification for water for laboratory use (Identical) ISO 5725:1986BS 5497 Precision of te
11、st methods Part 1:1987 Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (Identical) ISO 7513:1990BS 6986 Analysis of instant tea Part 3:1990 Method for determination of moisture content (loss in mass at 103 C) (Identical) ISO 7516:
12、1984Part 1:1988 Methods of sampling (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will
13、be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 13:29:34 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7820-1:1995 BSI 10-19991 1 Scope This International Standard specifies a method for the determin
14、ation of the caffeine content by high-performance liquid chromatography (HPLC) of teas and instant teas with a caffeine content of greater than 0,3 % (m/m) 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Internati
15、onal Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Mem
16、bers of IEC and ISO maintain registers of currently valid International Standards. ISO 1572:1980, Tea Preparation of ground sample of known dry matter content. ISO 3696:1987, Water for analytical laboratory use Specification and test methods. ISO 7513:1990, Instant tea in solid form Determination of
17、 moisture content (loss in mass at 103 C). 3 Principle Extraction of the caffeine from a test portion with water at 90 C in the presence of magnesium oxide. Filtration followed by determination of the caffeine content by high-performance liquid chromatography with ultraviolet detection. 4 Reagents U
18、se only reagents of recognized analytical grade, unless otherwise specified, and water in accordance with grade 1 of ISO 3696. 4.1 Methanol, HPLC grade. 4.2 Mobile phase, methanol/water mixture. Add 600 ml of the methanol (4.1) to a 2 litre one-mark volumetric flask. Dilute to the mark with water, m
19、ix, and filter the mixture through a filter of 0,45 4m pore size (5.3). NOTE 1By adjusting the methanol concentration, the retention time of the caffeine can be modified so as to optimize the HPLC separation. This can also be done by increasing the column temperature, but a temperature of 60 C shoul
20、d not be exceeded. 4.3 Ethanol/water mixture, 1/4 (V/V). 4.4 Magnesium oxide (so-called “dense magnesium oxide”). 4.5 Caffeine stock solution, corresponding to 0,500 g of caffeine per litre. Weigh, to the nearest 0,001 g, 0,125 g of caffeine into a 250 ml one-mark volumetric flask made of amber glas
21、s. Add sufficient ethanol/water mixture (4.3) to half-fill the flask. Swirl to dissolve the caffeine and then dilute to the mark with the ethanol/water mixture. This solution is stable for up to 1 month if stored in a refrigerator. 4.6 Caffeine standard solutions Standard solutions A and B shall be
22、prepared on the day of use. 4.6.1 Caffeine standard solution A, corresponding to 0,010 g of caffeine per litre (to be used for decaffeinated products). Allow the caffeine stock solution (4.5) to warm up to room temperature. Using a pipette, transfer 2,0 ml of the stock solution (4.5) to a 100 ml one
23、-mark volumetric flask. Dilute to the mark with water and mix. 4.6.2 Caffeine standard solution B, corresponding to 0,050 g of caffeine per litre (to be used for regular products). Follow the procedure given in 4.6.1 but take, using a pipette, 10,0 ml of the stock solution (4.5). 5 Apparatus Usual l
24、aboratory apparatus and, in particular, the following. 5.1 High-performance liquid chromatograph, equipped with an ultraviolet detector, allowing measurements to be made at a wavelength between 254 nm and 280 nm, and a chart recorder. NOTE 2A wavelength close to 280 nm is preferred since the maximum
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